<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      .outer {
        width: 700px;
        height: 400px;
        border: 1px solid #000;
        position: relative;
      }

      .con {
        width: 200px;
        height: 200px;
        background: pink;
        position: absolute;
        left: 0;
        top: 0;
        bottom: 0;
        right: 0;
        margin: auto;
      }
    </style>
  </head>
  <body>
    <div class="outer">
      <div class="con">con</div>
    </div>
  </body>
</html>
